A device is proposed that takes images of the same object (hereinafter simply referred to as an identical object) at the same time with two cameras for left and right eyes arranged side-by-side so as to generate a three-dimensional image (also referred to as a stereoscopic image) through the execution of various image processes to two image data (hereinafter, simply referred to as images) generated by the two cameras (see Patent Document 1).
A gap between images generated by overlapping the two images is referred to as a disparity. This disparity varies depending on a distance from cameras to an object.
For example, it is assumed that two cameras are disposed on a straight line with the optical axes of the cameras arranged in parallel to take images of an identical object. In this case, if the object is distant, the disparity of the object is substantially zero. As a distance between the cameras and the object is reduced, the disparity of the object increases. Therefore, if a three-dimensional image is generated and output for display based on two images including an object with a larger disparity, a projection amount of the object increases (appears closer) and a three-dimensional effect is enhanced.
However, if the disparity is increased greater than a certain level, an image sensed by the left eye is not fused with an image sensed by the right eye and a double image appears and makes the stereoscopic viewing impossible (fusional limitation). A double image due to an excessive disparity is known to cause visual fatigue. Therefore, to comfortably view a three-dimensional image, a depth (projection, depression) range of an object must be limited when the image is displayed. This limitation is disclosed in Non-Patent Literature 1.
For example, Patent Document 1 discloses a technique of generating a three-dimensional image without generating a double image due to an excessive disparity. In the technique disclosed in Patent Document 1, a depth range is nonlinearly controlled such that a three-dimensional image is displayed within a three-dimensionally viewable range of an observer, so as to generate an image easily three-dimensionally viewed by the observer.